JPH0575868A - Image processing device - Google Patents

Abstract

(57) [Summary] [Purpose] Efficiently compresses image data while preventing image deterioration. [Structure] A counter 129 for counting the amount of input image data
On the other hand, the counter 130 counts the amount of compressed data stored in the compression memory 111,
The compression parameter of the compression circuit 110 is set according to the count values of both counters.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to compression and expansion of color image data.

[0002]

2. Description of the Related Art Conventionally, when variable length coding is performed, the amount of code data for each block is made substantially constant,
The applicant has proposed a technique for keeping the code amount per screen constant.

[0003]

However, since neither the input amount of image data nor the amount of generated code data is taken into consideration, the memory for storing the code data cannot be used efficiently.

Therefore, an object of the present invention is to provide an image processing apparatus capable of efficient compression while maintaining good image quality.

[0005]

In order to solve the above-mentioned problems, the image processing apparatus of the present invention provides a means for inputting image data and an image data input by the input means according to a predetermined compression parameter. Compressing means, first means for measuring the amount of image data input by the input means, second means for measuring the amount of compressed image data compressed by the compressing means, and the first means. , And means for controlling the compression parameter of the compression means according to the measurement value of the second measurement means.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is an invention relating to color image compression / expansion. Especially JPEG (JointPhotograph)
ic Expert Group) A new method for connecting a method that solves the problems when a standard encoding method is used and a device with a constant-speed recording method such as an electrophotographic recording apparatus with good compatibility. Is provided.

In the JPEG encoding method, the quantization table and the Huffman table in one page are fixed, so that a photograph-like image having a low frequency component and a character image having a high frequency component are mixed in the original. The restored image was not always a good one. In color facsimiles and color DTP communication, it is natural that the above-mentioned mixed images are often present in the original document, and if such images are not properly restored, even if standardized encoding is adopted, it is difficult to use in this field. However, in the field of communicating and exchanging information with the other party such as color image coding, using a unique coding method impairs communication in a wide area, so it is a general idea to keep the standard method as much as possible. The present invention provides a new compression communication system that enables transmission of high image quality and high coding efficiency in the in-house mode, and also has a system capable of converting from the in-house mode for communication of the JPEG standard compression system.

Based on the above concept, the present invention uses a standard coding method for communication between different models, and if high-definition images are to be transmitted, the coding efficiency is lowered, and when high coding efficiency is required, The image quality is reduced and transmitted. If the other model is the same, it is possible to transmit high image quality and high coding efficiency in in-house mode.

In the embodiment of the present invention, the coding table is appropriately changed in 8 × 8 block units according to the image area determination amount indicating the type of image, and the image area information and the compressed data are stored. 1 if the communication partner requests compressed data in standard mode
An optimum encoding table is set based on the image area information for each page. Alternatively, the encoding table specified by the user from the operation panel is used. Once the encoding table is set,
Decompress using image area information and compressed data. The decompressed decompressed data is encoded in the standard mode using the encoding table described above without changing the table for one page. The encoded data is stored in another compressed page memory. The compressed data for one page is transmitted to the other party through the transmission path.

On the other hand, the recording speed is relatively high such as electrophotographic recording, and if one page of semiconductor real memory is provided for interfacing with a device requiring a constant recording speed, the cost becomes high and it becomes practical. Since it is not suitable, a method of storing in a compression memory, decompressing, and transmitting recording data to a recording device is used. At this time, the problem is that the fixed compression memory overflows in some cases and in other cases, the memory is left over because the amount of information of the image data transmitted from the host varies depending on the original and the image quality. Therefore, it is required to control the memory amount to be constant. Also in this case, we will consider both the original mode and the standard mode, and provide a method that allows mutual conversion. In other words, the compressed image stored in the host reduces the coding efficiency, improves the image quality, and sometimes has a large amount of data.
In some cases, the coding efficiency is improved and the data amount is small. Furthermore, the data amount of the same image differs depending on the compression method.
However, in a recording system such as electrophotographic recording that requires constant speed recording at the time of recording, image data for recording is usually recorded in a certain semiconductor memory and then transferred to an electrophotographic recording device. Therefore, if the compressed data coming from the host constantly changes, buffering for electrophotographic recording cannot be performed. The present invention enables the image data from the input scanner and the compressed or uncompressed data from the host to be recorded in high image quality in a constant buffering memory, so that the constant speed recording device can be connected inexpensively with a small amount of memory. A device is provided.

A method for realizing the present invention is to provide image position information of an original image (for example, address advancing degree), compressed data advancing degree (also address advancing degree), and image area information of 8 × 8 blocks to be compressed. The coding table for compressing the inside of the block is selected from the three. If the compression data progresses slower than the original image data, and the block to be compressed next is a gradation image with few high-frequency components, use the following encoding table, and use a table that greatly promotes compression efficiency. select. When the inside of the block is a character image or the like having a high frequency component, an encoding table is selected that slightly enhances the compression efficiency. Therefore, the optimum coding table determined from the intra-block image area also differs in the table actually coded by the memory control. Therefore, the image area information memory is modified by the memory amount control circuit. In this way, the amount of compression memory is kept constant regardless of the amount of information of the original image. The above is the outline of the constant memory control method.

Further, the method for realizing the present invention is such that the image position information (for example, the address advance) of the original image from the input device or the decompressed image from the host and the advance of the compressed data or the recompressed data (also the address). Of the image area information of the 8 × 8 block to be compressed, the coding table for compressing the inside of the block is selected. If the memory usage of the compressed data is faster than the processing progress of the uncompressed image data, that is, the compression efficiency is worse than the fixed memory amount, and the block to be compressed next is a gradation image with few high frequency components. If so, the next encoding table is selected, and a compression table that greatly enhances compression efficiency is selected. When the inside of the block is a character image or the like having a high frequency component, a compression table is selected which will slightly enhance the compression efficiency. Therefore, as the compression table, the table to be actually compressed is determined according to the intra-block image area information and the use speed of the compression memory for the progress of the input image. In this way, the amount of compression memory is kept constant regardless of the amount of original image information or the amount of image information from the host. The above is the outline of the constant memory control method of the present invention.

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the overall configuration of the image processing apparatus of this embodiment. In FIG. 1, reference numeral 1 is a color copying machine, which comprises a color scanner 101 and a color printer 102. It also has a controller for controlling both. Reference numeral 2 denotes a color copying machine interface, which is a color workstation 119 described later.
And the color copying machine 1 are connected to each other, and further processing such as trimming, compression, storage, decompression, and scaling of image data is performed therein. Video interfaces 103 and 122 connect the color copying machine 1 and the color copying machine interface 2 to communicate image data and command data, respectively. A trimming circuit 104 outputs the designated portion of the input image after 105. Similarly, when the image data is output, the designated portion is printed by the color printer 102.
For recording images. A conversion circuit 105 converts RGB data input from the color scanner 101 into rgb data in a standard color space.
It is composed of a table converter such as AM and ROM. 106
On the contrary, is a conversion circuit for converting rgb data in the standard color space into a YMCK signal matched with the color characteristics peculiar to the printer. This is also usually converted by a table converter. 10
A selector 7 selects the direction of input / output data. 108
Is a double buffer memory, and is basically composed of a line memory corresponding to the JPEG standard 8-line X pixel scanning width.
For example, 16 pel A4 3 colors, width 8 x 16
A memory of × 210 × 2 × 3 = 161.3 Kbytes is required. Reference numeral 109 is a circuit that frequency-converts image data for each 8 × 8 block by DCT (discrete cosine transform). Reference numeral 132 denotes an image area determination circuit that determines the type (character, photograph, halftone dot, etc.) of the original image for each 8 × 8 pixel block.

The image area judging circuit 132 can judge the image area by various methods such as a method of judging from the relationship between the DC portion and the AC portion of the DCT circuit 109. This image area determination amount gives a large value in an image region in which the target portion contains many high-frequency components such as character thin lines, and in an image region in which the frequency component is large in the low-frequency component such as the image region of the human face portion. Give a small value. As the image area determination amount, for example, 3-bit data is given. The memory 112 is thus judged 8
Image area determination data of × 8 block is stored. The memory amount of this portion is 2 × 210 × 16 × 8 / (8 × 8 × 2) =
A memory amount of 420 bytes is required. 110 is 1
This is a compression circuit that selects an optimum quantization table and Huffman table according to the image area determination amount of 32 and compresses by the JPEG ADCT method. That is, since a table that is in the image area of the block to be encoded is selected and encoded for each 8 × 8 block, the quantization table is not fixed standard encoding, but in order to improve image quality and encoding efficiency. It will be extremely effective. The compressed data and the image area information data in the memory 109 are stored in the compressed page memory 111 for one page and the image area information table 112 for one page. As will be described later, if the transmission partner is a host computer capable of decoding the above-mentioned unique compression method for switching the quantization table, the compressed data and the image area information data are transmitted to the host through the scsi interface 116. On the other hand, if the transmission partner is a host that cannot decode the original compression method, it is converted into the standard JPEG method and transmitted as follows.

Reference numeral 113 is a compressed data decompression circuit. At the time of decompression, the image area information table 112 is used, and the quantization table used for compression is identified. Therefore, at the time of decompression, the dequantization table corresponding to the table is used for decompression.

The decompressed and decompressed image data is written in the double buffer memory 108 while being scaled up and down by the scaling circuit. The written restored image is entirely compressed for one page using a quantization table designated manually or automatically. This method is a JPEG standard method.
The compressed data is transmitted to the host through 115 compression buffer memories and 116 SCSI. At this time, the image area information data 112 is not transmitted to the host side, but the compression table data for one page is transmitted. Reference numeral 119 denotes a host computer which constitutes a color workstation, and operates under a Unix or X-window environment. The language is, for example, the C language, 120 is a SCSI interface, and 121 is a software encoding software. An application program 124 controls the color copying machine 1 and the color copying machine interface 2. As a result, the color image from the color scanner 101 can be compressed and loaded into the host computer 119.

Reference numeral 117 is a controller for controlling each section of the color copying machine interface, and 118 is a command interpreter for analyzing a command from the color workstation and generating a control signal. In addition, for example, an error is notified to the host computer, and the whole operation is interlocked. 129, 130, 13
1 is a counter for measuring the amount of data, 132 is a selector for selecting one of the values of the counter 129 and the counter 131, 115 is data for controlling the amount of data according to the count values of the counters 129 to 131. It is a quantity controller. An operation unit 133 is used to manually select an encoding parameter (quantization table, Huffman table, etc.).

The processing performed by the above configuration will be described.

(1) Image Input from Color Scanner 101 The color scanner 101 includes R (red), G (green), and B (blue) line sensors, scans an original, and outputs 8-bit digital signals. To occur. The generated digital signal is input to the color copying machine interface 2 via the interface 103 in a dot-sequential RGB manner for each pixel.

(2) Internal Processing of Color Copier Interface 2 The RGB signal for each pixel input from the color scanner 101 is trimmed only in a necessary area by the trimming circuit 104, and the conversion circuit 105 r, g of the standard color space. , B signals, and at the same time, the r, g, and b signals are sent to the double buffer 108 as parallel signals. In the subsequent processing, similar processing is performed in parallel for each of the r, g, and b signals.

The counter 129 measures the amount of input image data.

(3) Data compression Data compression in this embodiment is basically performed as follows.

Variable length compression is used as the data compression algorithm. For example, JPEG (Joint
Photographic Expert Group
p) ADCT (Adaptive Discrete)
The image data is subjected to frequency conversion for each block as in the Cosine Transform) method, quantized by a predetermined quantization parameter, and then the DC component in the block is Huffman-coded for the prediction error, and the AC component is zigzag. Scan and perform Huffman coding.

The structure of the compression circuit 110 is shown in FIG.

In FIG. 2, 201 is a quantizer for linearly quantizing the input frequency transform coefficient, 202 is a ROM for storing the quantized coefficient, and 203 is Huffman coded for the quantized transform coefficient. It is a Huffman coding unit.

The quantized coefficients stored in the ROM 202 are an 8 × 8 two-dimensional matrix, and there are eight kinds of M ₁ to M ₈ . It is predetermined that the value of the quantization coefficient of the high frequency component increases as M ₁ approaches M ₈ , and the quantization step increases. These eight types of matrices are selected by the image area determination data (3 bits) from the image area determination circuit 132. As described above, by selecting the quantization matrix according to the property of the image to be compressed, it is possible to suppress the deterioration of the image quality and to perform the data compression with a high compression rate.

The above data compression is performed by the color scanner 10
It can be performed in parallel with the image reading by 1. The compressed image data is stored in the compression memory 111. At this time, the counter 130 measures the amount of data stored in the memory (empty capacity of the memory) by counting the address of the compressed memory.

On the other hand, the image area determination data for each block is stored in the memory 112.

(4) Data decompression Data decompression is performed by reversing the procedure for compressing the compressed image data stored in the compression memory 111 using the image area determination data for each block.

At this time, the counter 130 measures the amount of data stored in the memory (empty capacity of the memory) by counting the address of the compressed memory. On the other hand, the counter 131 measures the amount of expanded image data.

(5) Magnification / Demagnification The decompressed image data is magnified / magnified 114 as necessary.
Then, the scaling processing is performed and the data is sent to the double buffer. A loop is formed after the double buffer 108, and the same processing can be performed a plurality of times.

By providing this scaling circuit 114,
For example, it is possible to obtain a scaling factor that exceeds the scaling factor that is possible when the image is read by the color scanner 101.

(6) Image Area Judgment The image area judgment circuit 132 judges the characteristics of the input image (the degree to which it is a character or a photograph).

The determination is basically made by dividing the magnitude of the high frequency component of the transform coefficient, which is frequency-converted for each block in the DCT unit 109, into eight levels for each block.
In this way, 3 bits of image area determination data indicating the degree of being a character image with many high frequency components are generated.

The image area determination circuit 132 has a structure as shown in FIG. 301 is a high frequency component detection circuit, which is a DCT
Image area determination data indicating the magnitude of the high frequency component is generated by examining the AC portion of the conversion coefficient of. A determination data correction circuit 302 corrects the image area determination data according to a correction signal from the data controller 115.

When the image data is input from the color scanner 101, the data controller 115 monitors the count values of the counter 129 and the counter 130 and corrects it by comparing the input amount of the image data and the increase amount of the compressed data. Generate a signal.

For example, when the increase amount of the compressed data is large with respect to the input amount of the image data, the determination data is increased by 1 in order to increase the compression rate. That is, if the M ₅ table should be used, the M ₆ table is modified. The correction signal can be a multilevel signal according to the relationship between the input amount and the increase amount.

Similarly, when the amount of compressed data stored in the compression memory 111 is changed and then stored again in the compression memory 111, a correction signal is generated by comparing the count values of the counter 130 and the counter 131.

Further, the data amount controller 115 generates a correction signal according to the size information of the document input from the command interface 122 and sent through the controller 117. In this embodiment, the color scanner 101 reads A3 and the compression memory 111 also reads A3.
It has a capacity of one sheet. Here, for example, when an A4 original is read, the size information detected by the original size detection is sent to the data amount controller, and control is performed in consideration of the size information.

More specifically, since the color image data amount input from the scanner or the host computer is specified in advance, the total image data amount to be input can be calculated in advance. On the other hand, the amount of compressed image data memory is also fixed in terms of hardware, and is therefore fixed at a fixed value. For example, if the input image data amount is 10 Mbytes and the compression memory amount is 1 Mbytes, the input data can advance to 5 Mbytes and the compressed data amount is 0.6 Mbytes.
If it is bytes, it means that the compression efficiency is poor, and thereafter, a command is issued from 115 to increase the compression efficiency. Therefore, even if the image area determination circuit in 109 determines that the image is a high-frequency component image, the compression table is selected so as to enhance the compression efficiency even if the image quality is degraded as compared with the case where the command from 115 does not require high compression efficiency. Conversely, if the output data is 0.4 Mbytes even if the input data reaches 0.5 Mbytes,
For example, a compression table is selected so as to improve the image quality and reduce the compression efficiency even when an image with few high frequency components comes. In this way, the amount of compressed memory is controlled to be always constant regardless of the amount of information of the original image.

(7) Input from computer SCSI I / F1 is input from the host computer 119.
Raw image data compressed image data can be input via 16.

If the input is raw image data,
The data is sent from the SCSI I / F 116 to the double buffer 108, and the subsequent processing is as described above.

On the other hand, when the compressed image data is input, whether the compression changes the quantization parameter according to the image area as described above (hereinafter referred to as "unique mode"), or the quantization parameter Is processed in the following manner depending on whether it is constant (hereinafter referred to as "standard mode").

In the case of unique mode compressed data, SCS
The compressed image data is stored in the compression memory 111 through the I / F 116, and the image area determination data for each block is stored in the memory 112.

On the other hand, in the case of standard mode compressed data,
The compressed image data is stored in the compression memory 111, and the quantization table (one type) for one screen is stored in the memory 112. In this case, it can be expanded by the expansion circuit 113 once, compressed again in the unique mode, and stored again in the compression memory 111.

In particular, the amount of compressed image data for one screen is
When the capacity of the compression memory 111 is exceeded, it is recompressed so that one screen can be stored in the compression memory 111. The amount of compressed image data is sent from the host computer 119 to the command interpreter 118.

(8) Image Reproduction When reproducing an image based on the compressed data stored in the compression memory 111, real-time processing is performed in which the expanded image data corresponds to the recording speed of the color printer 102.

The restored image data that has been decompressed and scaled and then sent to the double buffer 108 is recorded in the color space conversion circuit 106 by the selector 107 and recorded color signals (Y, M, C,
K), and only the necessary portions are trimmed in the trimming circuit 104 and the video interface 10
3 to the color printer 102.

On the other hand, a control command for controlling recording start and the like is sent through the video I / F 122.

In this embodiment, a pair of photosensitive drums,
Since a multi-transfer type electrophotographic printer that repeats transfer of Y, M, C, K four times on the transfer drum is used, Y, M,
It is necessary to sequentially send the image data for one screen of C and K to the printer. Therefore, four times of four colors are read from the compression memory 111, and the Y, M, C, and
Data for one screen is output in the order of K.

(9) Output to Computer Raw image data and compressed image data can be output via the SCSI I / F 116.

Raw image data is sent from the double buffer 108 to the host computer 119 via the SCSI I / F 116.

On the other hand, in the case of compressed image data, the processing differs depending on whether the output destination computer accepts the compressed image data in the unique mode.

If the communication partner is a partner that accepts the unique mode, color image data of high image quality and high coding efficiency can be transmitted by transmitting this compressed data and compression table data. However, if the other party supports only the standard mode JPEG method, this data cannot be transmitted. Therefore, it is transmitted while being converted into the standard JPEG system by the following method.

Data compressed in the unique mode of one page and 8
Using the table information data of 112 determined from the information in the × 8 block and the compression memory progress information, the decompression circuit 113 decompresses and restores each 8 × 8 block. The decompressed data is stored in the double buffer memory 108 through the variable magnification circuit 114. The decompressed data is stored in 128 compression buffer memories by compressing the compression table by a certain table within one page,
Via SCSI as standard JPEG data to the host. This compressed data complies with the JPEG standard because one page is compressed with a fixed table. However, since the table is constant, the control for fixing the compression memory does not work, and it is not possible to write and record in the fixed one-page memory. However, in a computer having a hard desk such as a host computer, there is no problem even if the one-page memory amount varies slightly. A problem remains when a memory amount is fixed and a memory overflow occurs, such as a semiconductor memory.

In the above embodiment, compression is performed for each of the r, g, and b surfaces of the standard color space.
^{(L *, a *, b} *), (Y, C r, C b), (Y, I,
Q) or the like may be compressed separately for luminance and chromaticity. In that case, it is desirable to perform the image area determination based on the luminance signal.

Further, the printer is not limited to the electrophotographic system, and an inkjet thermal transfer system may be used. Further, it may be a printer (bubble jet printer) using a head of a type that ejects droplets by utilizing film boiling due to thermal energy.

The compression method is not limited to the ADCT method. In addition to the quantization parameter, the Huffman table coefficient may be changed as the compression parameter.

[0060]

As described above, according to the present invention, efficient image compression can be performed without degrading the image quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a compression circuit.

FIG. 3 is a block diagram showing a configuration of an image area determination circuit.

[Explanation of symbols]

 110 compression circuit 111 compression memory 115 data amount controller 132 image area determination circuit

Claims (5)

[Claims] 1. A unit for inputting image data, a unit for compressing the image data input by the input unit according to a predetermined compression parameter, and a unit for measuring the amount of image data input by the input unit. 1 means, 2nd means for measuring the amount of compressed image data compressed by said compression means, and controlling the compression parameter by said compression means according to the measurement values of said 1st and 2nd measurement means An image processing apparatus comprising: 2. The image data input by the input unit and the image data compression by the compression unit are performed in parallel, and the control unit controls the compression parameter in real time at predetermined intervals. The image processing apparatus according to claim 1. 3. The image processing apparatus according to claim 1, wherein the control unit controls the compression parameter so that the amount of compressed image data for one screen is constant regardless of the input image. 4. The image data input by the input means is compressed image data, and the compression means decompresses the compressed image data input by the input means and then re-compresses the compressed image data. The image processing device according to claim 1. 5. The image processing apparatus according to claim 1, wherein the compression parameter is a quantization parameter.